1. Field of the Invention
The present invention relates to apparatus used to position and deploy medical diagnostic and treatment devices in a body.
2. Discussion of the Related Art
A growing number of medical diagnostic and treatment devices are being developed that are remotely used to assess and/or treat patients, typically being guided to a target site using imagining technology such as fluoroscopes or ultrasound. Such devices include stents, stent-grafts, balloons, blood filters, occluders, probes, valves, electronic leads, orthopedic devices, etc. Usually these devices are mounted near the end of a catheter or guidewire and are remotely steered to the targeted site. Radiopaque markers or similar indicia are often used to allow the medical staff to exactly position the medical device using the imagining technology.
Once properly positioned, the medical staff will then carry out the procedure and/or deploy the necessary device or devices. Since most of these procedures, such as interventional treatment of occlusions or aneurysms, require exact placement of a treatment device, it is important that the device deploys in the same position where it had been initially placed. For instance, in treating aortic aneurysms with a stent-graft, physicians expect displacement of the device of less than 5 mm following deployment. Any greater displacement may result in endoleaks, blocked side vessels, or other complications requiring otherwise unnecessary further treatments or even risky conversion to open surgery.
Not surprisingly, numerous apparatus have been proposed to facilitate the placement of such devices. Originally self-expanding devices were simply drawn or stuffed into a catheter tube and then pushed out at the treatment site. Exact placement using this method can prove somewhat elusive, with the medical staff often required to deploy and retract the device repeatedly before the correct orientation is achieved.
More exacting deployment methods have since been developed, such as employing various constraining cords, e.g., those described in U.S. Pat. No. 6,042,605 to Martin et al., or implantable constraining sheaths, e.g., those described in U.S. Pat. No. 6,352,561 to Leopold et al.
A similar concept to the original catheter tube constraint is to use a thin sheath of material that is pulled back over the treatment device while holding the device in place. One advantage of this concept is that the device and thin sheath can take up considerably less space than housing a device within a relatively bulky catheter tube. The thin sheaths also can provide greater flexibility over much stiffer catheter tube materials. Such compactness and flexibility are highly desirable as physicians try to reach tighter treatment sites through smaller and more tortuous vessels. Unfortunately, this method can put considerable strain on a self-expanding device, which is exerting pressure against the constraining sheath throughout the deployment process. The resulting friction between the device and the sheath often requires application of considerable tensile force to remove the sheath, making ultimate exact positioning much more difficult, as well as possibly damaging the treatment device in the process of sheath removal.
One deployment method to limit such effects is to employ a thin sheath of material that is everted over itself, so that the constraining sheath rubs only against itself while it is being pulled back over a self-expanding device. In other words, a sheath of a given diameter is everted back over itself and then pulled down the length of the sheath through the deployment procedure. Variations on this concept are described in, for instance, U.S. Pat. No. 4,732,152 to Wallsten, U.S. Pat. No. 5,571,135 to Fraser et al., U.S. Pat. No. 6,942,682 to Vrba et al., and US Application 2006/0025844 to Majercak et al., and US Patent Application 2006/0030923 to Gunderson. With sufficiently thin and strong sheath materials, these methods offer the prospect of compactness with less strain placed on the treatment device and perhaps more precise device placement.
While everting sheaths address some of the complications seen with non-everting sheaths, they still can require considerable tension in order to pull the sheath over itself and the self-expanding device during deployment, resulting mainly from the friction of everted portion of the sheath rubbing against the non-everted portion of the sheath while the sheath is being removed. These concerns are compounded with longer device lengths and more robust self-expanding devices that exert greater outward pressures. The greater the tension needed to evert and remove the sheath, the more demanding it is for the medical staff to remove the sheath while trying to hold the apparatus in its exact position during deployment. Increased deployment tensions also require more substantial sheath constructions so as to avoid sheath and deployment line breakage during deployment. It is believed that these deficiencies of everting sheaths may have limited practical applications for such deployment methods.
Accordingly, it would be desirable to develop a deployment apparatus that retains many of the benefits of everting sheath deployment while allowing for lower deployment tensions and more exact device placement.